1. Field of the Invention
The present invention relates to a method for measuring at least one of ground contact pressure, shear stress, and an amount of skidding of a tire.
2. Description of the Related Art
Conventionally, for evaluating the performance of a tread surface of the tire, the ground contact pressure, shear stress, and amount of skidding of the tire are measured. For the measurement, a measurement point is set on the tread surface of the tire and the tire is made to roll on a flat, measuring board under a predetermined condition. The measurement point on the tread surface is made to contact with a sensor embedded in the flat board. Before actual measurement, an alignment process is performed. In the alignment process, the measurement point on the tire tread surface is made to perfectly coincide with the position of the sensor arranged on the flat board. One known example of the alignment process is described in Japanese Patent Application Laid-Open No. H3-78636 which discloses a method for measuring the ground contact pressure of the tire.
According to the method disclosed in Japanese Patent Application Laid-Open No. H3-78636, a tread surface of a tire is marked with a chalk or a colorant to indicate the position of a measurement point. Then, the tire is placed at the running start position on the flat board. In the middle of the flat board, a measurement plate is arranged movable with respect to the flat board. A pressure sensor is embedded in the measurement plate at the center thereof to detect the ground contact pressure of the tire. The tire is made to undergo preliminary running from the running start position toward the measurement plate, thus, the mark of the measurement point on the tire is transferred to the measurement plate. The misalignment between the position of the pressure sensor and the position where the mark of measurement point is transferred is read in terms of X coordinate and Y coordinate. Here, X direction refers to a running direction of the tire, and Y direction is a direction perpendicular to the X direction (i.e., a direction parallel to the rotation axis of the tire). After placed at the running start position again, the tire is moved in X direction by a shift amount Δx, and the measurement plate is moved in the Y direction by a shift amount Δy. Thus, the misalignment is corrected. Thereafter, the tire is made to undergo main running towards the measurement plate and the ground contact pressure is measured.
When the method of Japanese Patent Application Laid-Open No. H3-78636 is employed, the running start position of the tire is moved by shift amount Δx in the X direction before the main running. Hence, the running distance between the running start position and the pressure sensor changes in the main running from that in the preliminary running. Therefore, even though the misalignment of the tire in the X direction is corrected, the measurement point does not always reach the position of the sensor depending on the influence of the driving/braking force applied to the tire, and errors occur, resulting in low reproducibility.